Cleavage of zygote begins in a few hours after fertilization. It lasts for several days, and by the middle of the sixth day the embryo already has mo

Cleavage of zygote and embryo implantation

Cleavage of zygote begins in a few hours after fertilization. It lasts for several days, and by the middle of the sixth day the embryo already has more than 100 cells. Zygote cleavages by mitosis so that each of its daughter cells have 46 chromosomes. However, in contrast to somatic cells, all daughter cells of zygotes arranges within its shell, that is, it does not increase. With each cleavage of zygote increases the number of cells and their size reduces.

On the seventh day after fertilization, the embryo begins to implant in the uterine wall, forming the primary villi. This is a very important process — the connection of the embryo with the mother — which is called implantation (from Latin “plantation” -“transplant”) (diagram 124). Embryonic cells have enzymes that partially destroy the uterine lining (endometrium) and a mucosa of vessel. The embryo surrounds by the blood that flows from the damaged blood vessels, and starts getting nutrients and oxygen from blood. Since then, the germ cells, which “breathed” anaerobic way (oxygen-free), are switching to aerobic (oxygen) respiration. After implantation begin the embryo growth and differentiation processes of its cells. Of their certain parts form extraembryonic structures — embryonic membranes, while others create the fetus, i.e. embryonic shield. Taken from http://worldofschool.org

Diagram 124. Diagram of a fertilized ovum development: 1 — a mature egg; 2 — fertilization; 3-5 — cleavage; 6 — implantation; 7 — sperm
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Questions:
  • Explain the biological mechanisms of embryo implantation.